Sudo button is always visible in the "on" state for users who do NOT have sudo access.

The logic to determine whether to subvert the display of the "sudo" button uses is_array to test $sudo_roles, which presumably used to be FALSE when there were no sudo roles available, but which now returns array() in such a case. This patch corrects the problem by replacing is_array() with !empty(); however, there is a php oddity in that variable assignment is allowed within is_array(), but it is disallowed within a call to empty(). This patch therefore needed to increase the verbosity of the existing code slightly. The form chosen was selected to minimize the size of the resulting diff; a nested-if structure might be more pleasing for the final result.